1. Field of the Invention
This invention generally relates to fluid flow devices and, more specifically, to the use of multiple sample injection needles in a flow cytometer.
2. Description of the Related Art
The following descriptions and examples are not admitted to be prior art by virtue of their inclusion within this section.
Spectroscopic techniques are widely employed in the analysis of chemical and biological systems. Most often, these techniques involve measuring the absorption or emission of electromagnetic radiation by the material of interest. One such application is in the field of microarrays, which is a technology exploited by a large number of disciplines including the combinatorial chemistry and biological assay industries. Luminex Corporation of Austin, Tex., has developed a system in which biological assays are performed on the surface of variously colored fluorescent microspheres. Contemporary flow cytometers using these microspheres can test for tens to over one hundred different analytes in a biological sample and future increases are probable. While the ability to test for large numbers of analytes has improved, the fluid handling of a sample for examination has surfaced as an impediment to productivity.
In a typical flow cytometer, a sample is aspirated into the flow cytometer using a positive displacement pump and a network of tubing and valves. The sample is then injected through a sample injection needle into an interrogation flow cell (e.g., cuvette) which hydrodynamically focuses the sample via a sheath fluid. This focusing technique serves to separate particles for individual interrogation and confines the particles to a known location in the flow cell. In many cases, the sample injection needle is centrally positioned within the interrogation flow cell such that a sample may be introduced and focused within a central portion of an encompassing sheath fluid. Such a configuration has generally limited flow cytometers to have only one sample injection needle within the interrogation flow cell as multiple injection needles would constitute at least some of the needles to be off center, hindering the focus of fluid dispensed therefrom. As a consequence, throughput of flow cytometers is generally limited. In addition, a single injection needle configuration requires assays to be fully prepared prior to being injected into an interrogation flow cell, increasing time and money for analyzing a sample and further limiting the application of the flow cytometers to fully prepared assays.